The present invention relates to analytical instruments for detecting hazardous materials, and in particular to portable instruments.
This invention relates to analytical devices and, more particularly, to devices for detecting the presence of at least one pollutant or other hazardous component in a fluid sample. Such devices are needed, for example, in hazardous waste activities, such as site surveys to determine the presence of pollutants, location and identification of contamination, as well as certification of the absence of contamination (e.g. during transport and storage of wastes), monitoring of waste streams, and maintenance and operation of facilities. Hazardous wastes may include a large number of different materials. Detection devices are known for detecting and measuring one or a few selected pollutants, but they are not designed to identify unknown pollutants. When a gas for analysis may contain an unknown pollutant, it is usually necessary to obtain a sample of the gas and send it to a laboratory for a remote analysis, a costly and time-consuming operation.
In the aforementioned copending U.S. application Ser. No. 585,699, there is disclosed a low-power, portable, analytical device for identifying hazardous components in a gas, such as air, through the use an array of small sensors, such as electrochemical sensors, to provide a pattern of responses which is compared to a library of previously established response patterns to provide an identification of a component of the gas. The array also includes at least one heating filament capable of producing one or more derivatives by oxidation or pyrolysis of the component, so that the device is usable for detecting electrochemically inactive components. In addition, the responses from the sensors may be varied by changes in one or more of the operational conditions, such as voltage, temperature, sample flow rate, or diversion of the sample through a selective chemical filter and the like, so that the number of different responses is greater than the number of sensors and the number of detectable components in the gas. Analysis of the responses also provides data on the concentration levels of the hazardous component or components. That device has afforded adequate sensitivity for detecting hazardous components in concentrations as small as 1 ppm (parts per million).
But it is frequently necessary to detect certain hazardous components, such as certain organic chemicals, in trace amounts down to levels of one ppb (parts per billion) or less in complex mixtures. Techniques exist for analyzing such organic chemicals, but they are expensive and time consuming and require transport of samples to the laboratory. For example, gas chromatographic methods have been utilized, but it has been found that high column temperatures and, thus, large power outputs are required for efficient separation of organic chemicals such as primary aromatic amines. Furthermore, the primary aromatic amines must be absorbed or condensed from the air samples to improve the sensitivity of the assay. Once the sample is absorbed or condensed, it has to be flash-volatilized into the chromatography column. This procedure also consumes large amounts of energy. The large power requirements for such gas chromatography are not feasible in a portable instrument.
It has been suggested that a liquid chromatograph may be combined with electrochemical detectors, such an approach being disclosed in U.S. Pat. No. 4,511,659. But that arrangement uses standard analytical chromatography techniques utilizing large chromatographic columns, typically well in excess of 10 cm. in length, the system not being suitable for use in a portable instrument.
Small (3 cm.) chromatographic columns are known, but they are typically used for "cleanup" operations, serving as disposable pre-filters for separating certain chemical components prior to passing them through a large analytical chromatographic instrument. Such small devices have not heretofore been recognized as being capable of providing the high resolution necessary for an analytical instrument. Rather, it has been recognized that to increase resolution it is generally necessary to provide longer chromatographic columns, higher pressures and higher energy consumption, all of which detract from portability and field operation.